Abstract: The West Coast Region includes the onshore part of the South Island west of the Alpine Fault and the Waimea-Flaxmore Fault System, and the adjacent continental shelf south of 40 deg. 20' S. The data-base used in this study includes geological, gravity, and aeromagnetic maps at a scale of 1:250 000 covering the entire onshore part of the region; more detailed geological maps of most of the areas underlain by Cretaceous and Tertiary sediments; reconnaissance seismic surveys of the continental shelf and some onshore areas; and 163 stratigraphic columns derived from surface sections and drillholes. The large amount of structural and stratigraphic information available is synthesised in four sheets of maps showing the coverage of data, major structural features, data derived from seismic interpretation, and a series of isopach and paleogeographic /lithofacies maps for different times from Early Cretaceous to the present day. Pre-Cretaceous rocks range in age from Late Precambrian to Jurassic, and include a variety of igneous, metamorphic, and sedimentary lithologies that were formed while New Zealand was still a marginal part of Gondwana. The Cretaceous and Cenozoic sedimentary sequence records the rifting and separation of the New Zealand continental block from Gondwana (Cretaceous to Paleocene), and later movements on the boundary between the Indian and Pacific plates that cuts obliquely through the South Island (Alpine Fault). Most of the Early Cretaceous is not represented by a sedimentary record, but K-Ar dating and stratigraphic evidence indicate a period of plutonic and volcanic activity beginning at about 110 m.y. that was immediately followed by rapid uplift, erosion, and deposition of coarse alluvial sediments in Late Albian (Motuan-Ngaterian) time. Apart from a single isolated occurrence of fluvial sediments there is no sedimentary record for the 20 m.y. period between Cenomanian and Campanian (Arowhanan-Piripauan stages). K-Ar dates of 90-78 m.y. on basalt and lamprophyre dikes indicate a period of basaltic magma emplacement.